The present invention relates to a multi-layer printed board having integrated circuits or large scale integrated circuits.
The multi-layer printed board with integrated circuits or large scale integrated circuits is likely to generate electromagnetic noises which cause malfunctions of internal electronic elements such as transistors in the integrated circuits or the large scale integrated circuits or external electronic elements. The generation of the electromagnetic noises seems to be caused by electromagnetic radiation in a common mode due to a current caused by parasitic capacitance of the circuits and parasitic inductance thereof as well as due to a high frequency current flowing through a power supply line. The mechanism of generation of the electromagnetic noises is somewhat complicated, for which reason it was difficult to resolve the problems with generation of the noise. In the prior art, it was proposed to form magnetic films on both surfaces of the printed board for enabling the magnetic films to absorb the electromagnetic noises. This is disclosed in Japanese laid-open patent publication No. 6-244581. It was also proposed to form shielding layers on both surfaces of the printed board for enabling the shielding layers to shield the electromagnetic noises. This is disclosed in Japanese laid-open patent publication No. 6-244582. It was further proposed to form absorption layers on both surfaces of the printed board for enabling the absorption layers to absorb the electromagnetic noises. This is disclosed in Japanese laid-open patent publication No. 2-87593. The above conventional multi-layer printed boards as proposed are, however, incapable of suppressing the generation of the electromagnetic noises.
Still another conventional multi-layer printed board was proposed wherein a high voltage layer, a ground layer and a signal layer are laminated to be separated by insulation layers, which will be described with reference to FIG. 1A. A power is supplied through the high voltage layer to the integrated circuits or the large scale integrated circuits. An IC/LSI circuit 3 is connected between a high voltage line 22 through which a power is supplied from a power source to the IC/LSI circuit 3 and a ground line 23. A de-coupling capacitor 4 is also provided which is connected in parallel to the IC/LSI circuit 3 and between the high voltage line 22 and the ground line 23. A high frequency power source current flows through the high voltage line 22. The high frequency power source current is by-passed through the de-coupling capacitor 4. The de-coupling capacitor 4 also serves to suppress variation in potential of a power terminal of the IC/LSI circuit 3.
On the other hand, in the multi-layer printed board, a power supply layer serves as the power supply line 22 and comprises an electrically conductive layer which is flat, so as to ensure a large area for current flow thereby reducing a resistance of the power supply layer. The reduction in resistance of the power supply layer makes it easy to suppress the variation in voltage of the direct current power supply.
For the above conventional multi-layer printed board, it is difficult to control the high frequency power current flowing through the power source circuit layer with operations of the IC/LSI circuit. If the power source circuit layer is flat to reduce its impedance, then the high frequency power source current of the IC/LSI circuit will flow through not only the de-coupling capacitor of one of the IC/LSI circuits but also the other de-coupling capacitor of another IC/LSI circuit, for which reason the distribution of the high frequency power source current is complicated very much, resulting in difficulty in analyzing the distribution. This means that it is difficult to determine the capacitance of the de-coupling capacitors provided in individual IC/LSI circuits.
Since the power source circuit layer is flat and current paths of the high frequency power source current having flowed into the power source circuit layer are complicated. In a case, a large loop of current is formed, which irradiates an electromagnetic wave and deteriorates immunity of the circuit.
For example, as illustrated in FIG. 1B, there are provided three IC/LSI circuits 3C, 3D and 3E which are individually connected between a high voltage line 22 through which a power is supplied from a DC power source to the IC/LSI circuit 3C and a ground line 23. A de-coupling capacitor 4D with a large capacitance and a small impedance is connected in parallel to the IC/LSI circuit 3C and between the high voltage line 22 and the ground line 23. A de-coupling capacitor 4E with a middle capacitance and a middle impedance is connected in parallel to the IC/LSI circuit 3D and between the high voltage line 22 and the ground line 23. A de-coupling capacitor 4F with a small capacitance and a large impedance is connected in parallel to the IC/LSI circuit 3E and between the high voltage line 22 and the ground line 23. Since the de-coupling capacitor 4F connected in parallel to the IC/LSI circuit 3E has a large impedance, then the high frequency power source current from the IC/LSI circuit 3E is partially by-passed through the de-coupling capacitor 4F to the ground line 23 and remaining parts of the high frequency power source current from the IC/LSI circuit 3E may flow into the other IC/LSI circuits 3C and 3D. This results in enlargement in area of the current loop whereby the irradiated electromagnetic noises are increased and the immunity of the circuit is deteriorated. If, however, the high frequency power source current is not by-passed through the de-coupling capacitor connected in parallel to the IC/LIS circuit, then the high frequency power source current flows into the other current paths whereby the impedance of the current paths increases, resulting in an increased variation of the alternating current voltage. The large variation in the alternating current voltage might prevent the IC/LSI circuit from performing stable operations.
As described above, the above conventional multi-layer printed board is incapable of suppressing the generation of the electromagnetic noises. This means that the above conventional multi-layer printed board is incapable of complete shielding of the electromagnetic wave. It was proposed to accommodate the electronic component in a metal box in order to shield the electronic component from the electromagnetic noise. It is, however, required to form an opening in the metal box for an operational unit. The opening of the metal box allows a leakage of electronic noise.
Whereas it was proposed to form an inductor between the IC/LSI circuit and a power source circuit layer as illustrated in FIG. 2, wherein inductors 15 are provided on a surface of the multi-layer printed board so that the inductors 15 are connected through via holes 13 and through holes 14.
The above proposal for providing the inductors 15, however, results in the following problem. A distance between the power source layer 7 and the IC 3 is long, for which reason the generated noises are irradiated toward other signal lines. If, further, a chip inductor is provided on the printed board surface for every power source terminals of the integrated circuits, then this results in substantive reductions in free area of the printed board surface and in three-dimensional space in the multi-layer printed board. Such reductions render it difficult to provide via holes or through holes through which the chip inductors provided on the printed board surface are connected to the integrated circuits. Particularly, in the high frequency and high speed devices, several tens or a few hundred power source terminals are provided for every integrated circuit. This means it is difficult practically to provide, on the printed board surface, a large number of chip inductors individually correspondent to the power source terminals.
In the above circumstances, it had been required to develop a novel multi-layer printed board free from the above problems.